hey ;o)

• use 100 or 50 iso if possible
• work in raw if possible
• don't zoom too much
• close two aperture to obtain the best of the lense
• don't shoot without tripod if the speed is less than your focal (ie. shoot at 1/60è s. with a 50mm, may be 1/30è, but sharpnes is not guaranteed anymore - 135mm -> 100è s or 200è s, etc)

in photoshop, use the 'unsharp mask' ... but be cool with it !!!!

last, could you please put a sample here ?

hope this help !